WAEC Chemistry 2021 Theory — Question 23

Model answer

(i) I. Graphite has a hexagonal (layered sheet) structure. II. Diamond has a tetrahedral (giant covalent, 3-D network) structure. (ii) In diamond, each carbon is covalently bonded to four others in a rigid interlocking 3-D network, giving it hardness; all four valence electrons are localised in covalent bonds so there are no free/mobile electrons, making it a non-conductor. In graphite, each carbon is bonded to only three others, forming flat sheets held together by weak Van der Waals forces that can slide over each other (making it soft); one valence electron per atom is delocalised and free to move, allowing graphite to conduct electricity.